Return a different error from Invalid Password when a user is deactivated (#5674)

Return `This account has been deactivated` instead of `Invalid password` when a user is deactivated.

synapse/api/errors.py

@@ -139,6 +139,22 @@ class ConsentNotGivenError(SynapseError):
         return cs_error(self.msg, self.errcode, consent_uri=self._consent_uri)
 
 
+class UserDeactivatedError(SynapseError):
+    """The error returned to the client when the user attempted to access an
+    authenticated endpoint, but the account has been deactivated.
+    """
+
+    def __init__(self, msg):
+        """Constructs a UserDeactivatedError
+
+        Args:
+            msg (str): The human-readable error message
+        """
+        super(UserDeactivatedError, self).__init__(
+            code=http_client.FORBIDDEN, msg=msg, errcode=Codes.UNKNOWN
+        )
+
+
 class RegistrationError(SynapseError):
     """An error raised when a registration event fails."""